The present invention relates to a photoresist polymer that is employed in a photolithography process for the manufacture of a semiconductor device, more specifically, a photolithography process using extremely short wavelength-light such as ArF and KrF, which would be applied to the manufacture of 1 G or 4 G DRAM semiconductor devices.
Recently, the trend towards the high integration of semiconductor devices has accelerated, and this is much affected by the development of techniques for forming a micro-pattern using photoresist polymers. In order to prepare a micro-pattern, a minute pattern is formed on a photoresist (hereinafter, sometimes abbreviated as xe2x80x9cPRxe2x80x9d), which is widely used as a mask in a preparation of a semiconductor device, and therefore a suitable photoresist is an indispensable requirement for these processes.
Up to the present time, methods that have been suggested for forming an ultramicroscopic pattern of not more than 0.5 xcexcm include: (1) a contrast enhancement layer (here-in-after, abbreviated to as xe2x80x9cCELxe2x80x9d) method wherein an additional film is formed on a wafer to enhance the image contrast, (2) a method of using a phase reversal mask, and (3) a method of silylating the surface of a PR film. However, these methods have several disadvantages, such as complicated processes and insufficient yield.
A popular method of increasing the resolution of the PR pattern is to use a light source of the deep ultraviolet band of the light spectrum (hereinafter referred to as xe2x80x9cDUVxe2x80x9d) which requires a PR polymer adapted for use with such a light source.
A chemical amplified-type PR composition, which is prepared by blending a photoacid generator (PAG) and a polymer having a structure of sensitively reacting with an acid, are widely used as a PR for DUV. According to the reaction mechanism of the chemical amplified-type PR, the photoacid generator generates acid when it is illuminated by the light source, and substituents on the main chain or branched chain of the PR polymer are decomposed or crosslinked in a reaction with the generated acid. This change in the polymer creates a solubility difference between the exposed portion and unexposed portion to the developing solution, to form a PR pattern. In view of the reaction mechanism, a PR for DUV, in particular for ArF radiation (193 nm), requires low light absorption at a wavelength of 193 nm, etching resistance, adhesiveness and developing ability in 2.38 wt % aqueous TMAH (tetramethylammonium hydroxide) solution.
Prior art research has been focused on novolac-type resins because of their high transparency at 193 nm and good etching resistance. As an example of such research, the compound represented by Chemical Formula 1 shown below has been developed by Bell Laboratory. 
However, the xe2x80x98Axe2x80x99 portion of the compound (that is, maleic anhydride), which is employed to polymerize alicyclic olefin groups, is readily dissolved in 2.38 wt % aqueous TMAH solution even in unexposed regions of the PR film, so that a good pattern cannot be formed. In order to prevent the phenomenon, the amount of the monomer including the tert-butyl group (the xe2x80x98yxe2x80x99 portion) should be increased, but this results in relative decrease of xe2x80x98zxe2x80x99 portion and lowers adhesiveness with the substrate and sensitivity. In order to solve the problem, a cholesterol-type dissolution inhibitor has been added to the PR composition. However, since the amount of the dissolution inhibitor is typically very high [about 30%(w/w) of the resin], reappearance is low and the production cost are high, thereby making the composition unsuitable as a PR composition.
The present invention relates to a PR which solves the problems described above. The invention provides novel photoresist polymers having good etching resistance and adhesiveness, are developable in 2.38 wt % aqueous TMAH solution, and are suitable for a photoresist having high sensitivity, and a process for preparing the same. The present invention also provides photoresist compositions and semiconductor devices employing the novel photoresist polymers, and a process for preparing the same.
The present invention provides a novel photoresist polymer comprising a monomer represented by following Chemical Formula 2: 
wherein, R1 and R2 are independently xe2x80x94COOH or xe2x80x94Rxe2x80x94COOH; and R is a substituted or unsubstituted (C1-C10) alkyl.
The present invention also provides a photoresist polymer represented by the following Chemical Formula 100. 
wherein, R1 and R2 are independently xe2x80x94COOH or xe2x80x94Rxe2x80x94COOH; R is a substituted or unsubstituted (C1-C10) alkyl;
R3 is xe2x80x94COOR* or xe2x80x94Rxe2x80x2xe2x80x94COOR*; R* is an acid labile group; Rxe2x80x2 is a substituted or unsubstituted (C1-C10) alkyl;
R4 is H or R3;
R5 is a substituted or unsubstituted (C1-C10) alkyl; and
a, b and c are independently polymerization ratios of each comonomer.
In addition, the present invention also provides a photoresist composition containing (i) a photoresist copolymer of Chemical Formula 100 above, (ii) a photoacid generator, and (iii) an organic solvent.